Luma and chroma encoding using a common predictor

ABSTRACT

There are provided video encoders, video decoders, and corresponding methods. A video encoder for encoding video signal data for an image block includes an encoder ( 100 ) for encoding all color components of the video signal data using a common predictor ( 315 ). A video decoder for decoding video signal data for an image block includes a decoder ( 200 ) for decoding all color components of the video signal data using a common predictor ( 430 ). Additionally, an apparatus and method for encoding and decoding signal data for an image block includes an encoder and decoder for encoding/decoding color components of the video signal data without applying a residual color transform thereto. Furthermore, a video encoder and decoder for encoding/decoding video signal data for an image block includes an encoder and decoder for encoding/decoding the video signal data using unique predictors for each of color components of the video signal data.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/918,204, filed on Oct. 10, 2007 which claims the benefit, under 35U.S.C. §365 of International Application PCT/US2006/009990, filed Mar.16, 2006 which was published in accordance with PCT Article 21(2) onOct. 26, 2006 in English and which claims the benefit of U.S.provisional patent application No. 60/671,255, filed Apr. 13, 2005 andU.S. provisional patent application No. 60/700,834, filed Jul. 20, 2005.

FIELD OF THE INVENTION

The present invention relates generally to video encoders and decodersand, more particularly, to methods and apparatus for video encoding anddecoding.

BACKGROUND OF THE INVENTION

Presently, the 4:4:4 format of the International TelecommunicationUnion, Telecommunication Sector (ITU-T) H.264 standard (hereinafter the“H.264 standard”) only codes one of three channels as luma, with theother two channels being coded as chroma using less efficient tools.When an input to a codec is in the 4:4:4 format with full resolution inevery input component, coding two out of the three input components withthe less effective chroma coding algorithm results in the use of morebits in those two channels. This particular problem is more noticeablein intra frames. For example, the H.264 standard running in theIntra-Only mode is less efficient than JPEG2k for overall compressionquality at 40 dB (PSNR) and above.

Accordingly, it would be desirable and highly advantageous to havemethods and apparatus for video encoding and decoding that overcome theabove-described disadvantages of the prior art.

SUMMARY OF THE INVENTION

These and other drawbacks and disadvantages of the prior art areaddressed by the present invention, which is directed to methods andapparatus for video encoding and decoding.

According to an aspect of the present invention, there is provided avideo encoder for encoding video signal data for an image block. Thevideo encoder includes an encoder for encoding all color components ofthe video signal data using a common predictor.

According to another aspect of the present invention, there is provideda method for encoding video signal data for an image block. The methodincludes encoding all color components of the video signal data using acommon predictor.

According to yet another aspect of the present invention, there isprovided a video decoder for decoding video signal data for an imageblock. The video decoder includes a decoder for decoding all colorcomponents of the video signal data using a common predictor.

According to still another aspect of the present invention, there isprovided a method for decoding video signal data for an image block. Themethod includes decoding all color components of the video signal datausing a common predictor.

These and other aspects, features and advantages of the presentinvention will become apparent from the following detailed descriptionof exemplary embodiments, which is to be read in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood in accordance with thefollowing exemplary figures, in which:

FIG. 1 is a block diagram illustrating an exemplary video encodingapparatus to which the present principles may be applied;

FIG. 2 is a block diagram illustrating an exemplary video decodingapparatus to which the present principles may be applied;

FIG. 3 is a flow diagram illustrating an exemplary video encodingprocess with a pre-encoding, color transform block, in accordance withthe present principles;

FIG. 4 is a flow diagram illustrating an exemplary video decodingprocess with a post-decoding, inverse color transform block, inaccordance with the present principles;

FIG. 5 is a block diagram illustrating a simplified model of residualcolor transform (RCT);

FIGS. 6A and 6B are plots of average PSNR verses bit rate for ATVintra-only in accordance with the present principles;

FIGS. 7A and 7B are plots of average PSNR verses bit rate for CTintra-only in accordance with the present principles;

FIGS. 8A and 8B are plots of average PSNR verses bit rate for DTintra-only in accordance with the present principles;

FIGS. 9A and 9B are plots of average PSNR verses bit rate for MIR_HDintra-only in accordance with the present principles;

FIGS. 10A and 10B are plots of average PSNR verses bit rate for RTintra-only in accordance with the present principles;

FIGS. 11A and 11B are plots of average PSNR verses bit rate for STB_HDintra-only in accordance with the present principles;

FIG. 12 is a table illustrating H.264 sequence parameter syntax inaccordance with the present principles;

FIGS. 13A, 13B, 13C, and 13D is a table illustrating H.264 residual datasyntax in accordance with the present principles;

FIG. 14 is a flow diagram illustrating an exemplary video encodingprocess with a pre-encoding, color transform block, in accordance withthe present principles;

FIG. 15 is a flow diagram illustrating an exemplary video decodingprocess with a post-decoding, inverse color transform step block, inaccordance with the present principles; and

FIGS. 16A and 16B is a table illustrating H.264 macroblock predictionsyntax in accordance with the present principles.

DETAILED DESCRIPTION

The present invention is directed to methods and apparatus for videoencoding and decoding video signal data. It is to be appreciated thatwhile the present invention is primarily described with respect to videosignal data sampled using the 4:4:4 format of the InternationalTelecommunication Union, Telecommunication Sector (ITU-T) H.264standard, the present invention may also be applied to video signal datasampled using other formats (e.g., the 4:2:2 and/or 4:2:0 format) of theH.264 standard as well as other video compression standards whilemaintaining the scope of the present invention.

It is to be appreciated that methods and apparatus in accordance withthe present principles do not require use of any new tool(s) for theluma or chroma compression algorithm. Instead, the existing luma codingtools can be used. Accordingly, one advantageous result there from isthat the coding performance of the 4:4:4 format may be maximized whilepreserving backward compatibility and minimizing any change to theexisting H.264 (or other applicable) standard.

In accordance with the principles of the present invention as configuredin an embodiment, a luma coding algorithm is used to code all threecomponent channels of, e.g., 4:4:4 content. Advantages of thisembodiment include an improvement in the overall coding performance forcompressing 4:4:4 content with respect to the prior art. Presently, inthe existing H.264 standard, only one of three channels is coded asluma, and the other two are coded as chroma using less efficient tools.

Further, in accordance with the principles of the present invention asconfigured in an embodiment, color transformation is performed as apre-processing step. Thus, in accordance with this embodiment, aResidual Color Transform (RCT) is not performed inside the compressionloop. Advantages of this embodiment include the providing of consistentencoder/decoder architecture among all color formats.

Moreover, in accordance with the principles of the present invention asconfigured in an embodiment, the same motion/spatial prediction mode isused for all three components. Advantages of this embodiment includereduced codec complexity and backwards compatibility.

Also, in accordance with another embodiment, instead of using the samepredictor for all three components, a set (or subset) of three (3)restricted spatial predictors may be utilized for the three components.Advantages of this embodiment include an improvement in the overallcoding performance for compressing 4:4:4 content with respect to theprior art.

It is to be appreciated that the various embodiments described above andsubsequently herein may be implemented as stand alone embodiments or maybe combined in any manner as readily appreciated by one of ordinaryskill in this and related arts. Thus, for example, in a first combinedembodiment, a luma coding algorithm is advantageously used to code allthree component channels, color transformation is performed as apre-processing step, and a single predictor is used for all threecomponent channels. In a second combined embodiment, a luma codingalgorithm is advantageously used to code all three component channels,color transformation is performed as a pre-processing step, and a set(or subset) of three (3) restricted spatial predictors may be utilizedfor the three component channels. Of course, as noted above, othercombinations of the various embodiments may also be implemented giventhe teachings of the present principles provided herein, whilemaintaining the scope of the present invention.

The present description illustrates the principles of the presentinvention. It will thus be appreciated that those skilled in the artwill be able to devise various arrangements that, although notexplicitly described or shown herein, embody the principles of theinvention and are included within its spirit and scope.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the principlesof the invention and the concepts contributed by the inventor tofurthering the art, and are to be construed as being without limitationto such specifically recited examples and conditions.

Moreover, all statements herein reciting principles, aspects, andembodiments of the invention, as well as specific examples thereof, areintended to encompass both structural and functional equivalentsthereof. Additionally, it is intended that such equivalents include bothcurrently known equivalents as well as equivalents developed in thefuture, i.e., any elements developed that perform the same function,regardless of structure.

Thus, for example, it will be appreciated by those skilled in the artthat the block diagrams presented herein represent conceptual views ofillustrative circuitry embodying the principles of the invention.Similarly, it will be appreciated that any flow charts, flow diagrams,state transition diagrams, pseudocode, and the like represent variousprocesses which may be substantially represented in computer readablemedia and so executed by a computer or processor, whether or not suchcomputer or processor is explicitly shown.

The functions of the various elements shown in the figures may beprovided through the use of dedicated hardware as well as hardwarecapable of executing software in association with appropriate software.When provided by a processor, the functions may be provided by a singlededicated processor, by a single shared processor, or by a plurality ofindividual processors, some of which may be shared. Moreover, explicituse of the term “processor” or “controller” should not be construed torefer exclusively to hardware capable of executing software, and mayimplicitly include, without limitation, digital signal processor (“DSP”)hardware, read-only memory (“ROM”) for storing software, random accessmemory (“RAM”), and non-volatile storage.

Other hardware, conventional and/or custom, may also be included.Similarly, any switches shown in the figures are conceptual only. Theirfunction may be carried out through the operation of program logic,through dedicated logic, through the interaction of program control anddedicated logic, or even manually, the particular technique beingselectable by the implementer as more specifically understood from thecontext.

In the claims hereof, any element expressed as a means for performing aspecified function is intended to encompass any way of performing thatfunction including, for example, a) a combination of circuit elementsthat performs that function or b) software in any form, including,therefore, firmware, microcode or the like, combined with appropriatecircuitry for executing that software to perform the function. Theinvention as defined by such claims resides in the fact that thefunctionalities provided by the various recited means are combined andbrought together in the manner which the claims call for. It is thusregarded that any means that can provide those functionalities areequivalent to those shown herein.

Turning to FIG. 1, an exemplary video encoding apparatus is indicatedgenerally by the reference numeral 199. The video encoding apparatus 199includes a video encoder 100 and a pre-encoding color transform module105.

The pre-encoding color transform module 105 is for performing colorpre-processing of video signals prior to inputting the same to the videoencoder 100. The color pre-processing performed by the pre-encoding,color transform module 105 is further described herein below. It is tobe appreciated that the pre-encoding, color transform module 105 may beomitted in some embodiments.

An input of the pre-encoding color transform module 105 and an input ofthe video encoder 100 are available as inputs of the video encodingapparatus 199.

An output of the pre-encoding, color transform module 105 is connectedin signal communication with the input of the video encoder 100.

The input of the video encoder 100 is connected in signal communicationwith a non-inverting input of a summing junction 110. The output of thesumming junction 110 is connected in signal communication with atransformer/quantizer 120. The output of the transformer/quantizer 120is connected in signal communication with an entropy coder 140. Anoutput of the entropy coder 140 is available as an output of the videoencoder 100 and also as an output of the video encoding apparatus 199.

The output of the transformer/quantizer 120 is further connected insignal communication with an inverse transformer/quantizer 150. Anoutput of the inverse transformer/quantizer 150 is connected in signalcommunication with an input of a deblock filter 160. An output of thedeblock filter 160 is connected in signal communication with referencepicture stores 170. A first output of the reference picture stores 170is connected in signal communication with a first input of a motion andspatial prediction estimator 180. The input to the video encoder 100 isfurther connected in signal communication with a second input of themotion and spatial prediction estimator 180. The output of the motionand spatial prediction estimator 180 is connected in signalcommunication with a first input of a motion and spatial predictioncompensator 190. A second output of the reference picture stores 170 isconnected in signal communication with a second input of the motion andspatial compensator 190. The output of the motion and spatialcompensator 190 is connected in signal communication with an invertinginput of the summing junction 110.

Turning to FIG. 2, an exemplary video decoding apparatus is indicatedgenerally by the reference numeral 299. The video decoding apparatus 299includes a video decoder 200 and a post-decoder, inverse color transformmodule 293.

An input of the video decoder 200 is available as an input of the videodecoding apparatus 299. The input to the video decoder 200 is connectedin signal communication with an input of the entropy decoder 210. Afirst output of the entropy decoder 210 is connected in signalcommunication with an input of an inverse quantizer/transformer 220. Anoutput of the inverse quantizer/transformer 220 is connected in signalcommunication with a first input of a summing junction 240.

The output of the summing junction 240 is connected in signalcommunication with a deblock filter 290. An output of the deblock filter290 is connected in signal communication with reference picture stores250. The reference picture store 250 is connected in signalcommunication with a first input of a motion and spatial predictioncompensator 260. An output of the motion spatial prediction compensator260 is connected in signal communication with a second input of thesumming junction 240. A second output of the entropy decoder 210 isconnected in signal communication with a second input of the motioncompensator 260. The output of the deblock filter 290 is available as anoutput of the video decoder 200 and also as an output of the videodecoding apparatus 299.

Moreover, an output of the post-decoding, inverse color transform module293 may be available as an output of the video decoding apparatus 299.In such a case, the output of the video decoder 200 may be connected insignal communication with an input of the post-decoding, inverse colortransform module 293, which is a post-processing module with respect tothe video decoder 200. An output of the post-decoding, inverse colortransform module 293 provides a post-processed, inverse colortransformed signal with respect to the output of the video decoder 200.It is to be appreciated that use of the post-decoding, inverse colortransform module 293 is optional.

A description is now presented for enhanced 4:4:4 coding in accordancewith the principles of the present invention. A first describedembodiment is a combined embodiment in which the luma coding algorithmis used for all color components, the same spatial prediction mode isused for all color components, and the Residual Color Transform (RCT) isomitted from inside the compression loop. Test results for this combinedembodiment are also provided. Subsequently thereafter, a second combinedembodiment is described wherein the luma coding algorithm is used forall color components, a set (or subset) of restricted spatial predictorsis used for all color components (instead of a single spatial predictionmode), and the Residual Color Transform (RCT) is omitted from inside thecompression loop. Thus, a difference between the first and secondcombined embodiments is the use of a single spatial prediction mode forall color components in the first combined embodiment versus the use ofa set (or subset) of restricted spatial predictors for all colorcomponents in the second combined embodiment. Of course, as noted above,the embodiments described herein may be implemented as stand aloneembodiments or may be combined in any manner, as readily appreciated byone of ordinary skill in this and related arts. For example, inaccordance with the principles of the present invention as configured inan embodiment, only a single spatial prediction mode is used, withoutcombination with other embodiments such as the omission of RCT from thecompression loop. It is to be appreciated that given the teachings ofthe present principles provided herein, these and other variations,implementations, and combinations of the embodiments of the presentinvention will be readily ascertainable by one of ordinary skill in thisand related arts, while maintaining the scope of the present invention.

Turning to FIG. 3, an exemplary video encoding process with apre-encoding, color transform block, are indicated generally by thereference numerals 300 and 301, respectively.

It is to be appreciated that the pre-encoding, color transform block 301includes blocks 306, 308, and 310. Moreover, it is to be appreciatedthat the pre-encoding, color transform block 301 is optional and, thus,may be omitted in some embodiments of the present invention.

The pre-encoding, color transform block 301 includes a loop limit block306 that begins a loop for each block in an image, and passes control toa function block 308. The function block 308 performs colorpre-processing of the video signal data of the current image block, andpasses control to a loop limit block 310. The loop limit block 310 endsthe loop. Moreover, the loop limit block 310 passes control to a looplimit block 312, the latter being included in the video encoding process300.

The loop limit block 312 begins a loop for each block in the image, andpasses control to a function block 315. The function block 315 forms amotion compensated or spatial prediction of the current image blockusing a common predictor for each color component of the current imageblock, and passes control to a function block 320. The function block320 subtracts the motion compensated or spatial prediction from thecurrent image block to form a prediction residual, and passes control toa function block 330. The function block 330 transforms and quantizesthe prediction residual, and passes control to a function block 335. Thefunction block 335 inverse transforms and quantizes the predictionresidual to form a coded prediction residual, and passes control to afunction block 345. The function block 345 adds the coded residual tothe prediction to form a coded picture block, and passes control to anend loop block 350. The end loop block 350 ends the loop and passescontrol to an end block 355.

Turning to FIG. 4, an exemplary video decoding process with apost-decoding, inverse color transform block, are indicated generally bythe reference numerals 400 and 460, respectively.

It is to be appreciated that the post-decoding, inverse color transformblock 460 includes blocks 462, 464, 466, and 468. Moreover, it is to beappreciated that the post-decoding, inverse color transform block 460 isoptional and, thus, may be omitted in some embodiments of the presentinvention.

The decoding process 400 includes a loop limit block 410 that begins aloop for a current block in an image, and passes control to a functionblock 415. The function block 415 entropy decodes the coded residual,and passes control to a function block 420. The function block 420inverse transforms and quantizes the decoded residual to form a codedresidual, and passes control to a function block 430. The function block430 adds the coded residual to the prediction formed from a commonpredictor for each color component to form a coded picture block, andpasses control to a loop limit block 435. The loop limit block 435 endsthe loop and passes control to an end block 440.

In some embodiments, the loop limit block 435 optionally passes controlto the post-decoding, inverse color transform block 460, in particular,the loop limit block 462 included in the post-decoding, inverse colortransform block 460. The loop limit block 462 begins a loop for eachblock in an image, and passes control to a function block 464. Thefunction block 464 performs an inverse color post-processing of thevideo signal data of the current image block, and passes control to aloop limit block 466. The loop limit block 466 ends the loop, and passescontrol to an end block 468.

In the H.264 4:4:4 format, every component channel has full resolution.Thus, in accordance with the first combined embodiment set forth above,the luma coding algorithm is used on every color component to achievethe maximum overall compression efficiency. Accordingly, in theembodiment, for intra frames, every color component may be compressed,e.g., using those prediction modes listed in Table 8-2, Table 8-3, andTable 8-4 in ISO/IEC 14496 10 Advanced Video Coding 3^(rd) Edition(ITU-T Rec. H.264), ISO/IEC JTC1/SC29/WG11 and ITU-T SG16 Q.6, DocumentN6540, July 2004.

In addition, in the embodiment, the same spatial prediction mode is usedfor all three pixel components, to further reduce the complexity of thecodec and improve performance. For example, the prediction mode set bythe prev_intra4×4_pred_mode_flag, rem_intra4=4_pred_mode,prev_intra8×8_pred_mode_flag, and rem_intra8×8_pred_mode parameters forthe luma in the macroblock prediction header may be used by all threecomponents. Therefore, no extra bits and syntax elements are needed. Forthe B and P (predictive) frames, the reference pixels at fractionalpixel locations may be calculated by the interpolation methods describedin Section 8.4.2.2.1 of the H.264 standard for all three channels. Thedetailed syntax and semantic changes to the current H.264 standard arefurther discussed herein below.

Residual Color Transform (RCT) was added to the encoder/decoder in theHigh 4:4:4 Profile. As a result, the compression structure for the 4:4:4format is different from the one currently used in all of the otherprofiles in the H.264 standard for 4:2:0 and 4:2:2 formats. This resultsin some extra complexity to the implementation. Moreover, similar to anyother color transforms, YCOCG does not always improve the overallcompression performance. The effectiveness of YCOCG is highly contentdependent. Thus, to improve the overall compression and robustness, inthe embodiment, the color transform is placed outside of the predictionloop as a part of the preprocessing block. By doing this, selecting anoptimum color transform for a specific compression task is anoperational issue and the best answer for a particular input sequencecould be found among a number of options. In accordance with anembodiment where all three components are using the same spatialpredictors for the intra frames and the same interpolation filters forthe B and P (predictive or inter-coded) frames, having the colortransform performed on the prediction residues is identical toperforming the color transform on the source images outside of the codecwhen the rounding/truncation errors are ignored. This will be discussedfurther herein below. Thus, the RCT block is removed from the codingstructure to make the coding structure consistent among all of the colorformats.

Turning to FIG. 5, a simplified model of RCT is indicated generally bythe reference numeral 500. The RCT model 500 includes a reference pixelgenerator 510, a summing junction 520, and a linear transform module530. Inputs to the reference pixel generator 510 are configured toreceive motion/edge information and vectors [X₁], [X₂] . . . [X_(n)]. Anoutput of the reference pixel generator 510 is connected in signalcommunication with an inverting input of the summing junction 520, whichprovides prediction vector [X_(p)] thereto. A non-inverting input of thesumming junction 520 is configured to receive input vector [X_(in)]. Anoutput of the summing junction 520 is connected in signal communicationwith an input of the linear transform module 530, which provides vector[X_(d)] thereto. An output of the linear transform module 530 isconfigured to provide vector [Y_(d)].

In the simplified model of RCT 500, the color transform represented by a3×3 matrix [A] (a linear transform) is defined as follows:

$\begin{matrix}{\begin{bmatrix}Y \\u \\v\end{bmatrix} = {\lbrack A\rbrack \begin{bmatrix}R \\G \\B\end{bmatrix}}} & (1)\end{matrix}$

The [X_(in)], [X_(d)], [X_(p)], [X₁], [X₂] . . . [X_(n)] are 3×1 vectorsrepresenting the pixels in the RGB domain. The [Y_(d)] is a 3×1 vectorrepresenting the result of the color transform. Therefore,

[Y _(d) ]=[A][X _(d) ]=[A][X _(in) ]−[A][X _(p)]  (2)

Since, in the embodiment, the same spatial predictors and interpolationfilters are used for all three components in a macroblock in accordancewith the principles of the present invention as configured in anembodiment, the reference pixel [X_(p)] can be expressed as follows:

$\begin{matrix}{{\left\lbrack X_{p} \right\rbrack = {{\left\lbrack {X_{1}X_{2}X_{3}\mspace{14mu} \ldots \mspace{14mu} X_{n}} \right\rbrack \begin{bmatrix}c_{1} \\c_{2} \\c_{3} \\\ldots \\\ldots \\c_{n}\end{bmatrix}} = {\begin{bmatrix}R_{1} & R_{2} & {R_{3}\mspace{14mu} \ldots \mspace{14mu} R_{n}} \\G_{1} & G_{2} & {G_{3}\mspace{14mu} \ldots \mspace{14mu} G_{n}} \\B_{1} & B_{2} & {B_{3}\mspace{14mu} \ldots \mspace{14mu} B_{n}}\end{bmatrix}\begin{bmatrix}c_{1} \\c_{2} \\c_{3} \\\ldots \\\ldots \\c_{n}\end{bmatrix}}}},} & (3)\end{matrix}$

where a n×1 vector [C] represents the linear operations involved in thespatial predictors and interpolation filters defined in the H.264standard. Here, it is presumed that the reference pixel is calculated byusing a total number of n neighboring pixels [X₁], [X₂], . . . [X_(n)].

Substituting [Xp] in equation (3) into equation (2) results in thefollowing:

$\begin{matrix}{\left\lbrack Y_{d} \right\rbrack = {{\lbrack A\rbrack \left\lbrack X_{in} \right\rbrack} - {\lbrack A\rbrack {\left( {\begin{bmatrix}R_{1} & R_{2} & {R_{3}\mspace{14mu} \ldots \mspace{14mu} R_{n}} \\G_{1} & G_{2} & {G_{3}\mspace{14mu} \ldots \mspace{14mu} G_{n}} \\B_{1} & B_{2} & {B_{3}\mspace{14mu} \ldots \mspace{14mu} B_{n}}\end{bmatrix}\begin{bmatrix}c_{1} \\c_{2} \\c_{3} \\\ldots \\\ldots \\c_{n}\end{bmatrix}} \right).}}}} & (4)\end{matrix}$

Ignoring the rounding/truncation errors and assuming the same predictionmode is selected in either the RGB or Y domain results in the following:

$\begin{matrix}{\left\lbrack Y_{d} \right\rbrack = {{\lbrack A\rbrack \left\lbrack X_{in} \right\rbrack} - {\left( {\lbrack A\rbrack \begin{bmatrix}R_{1} & R_{2} & {R_{3}\mspace{14mu} \ldots \mspace{14mu} R_{n}} \\G_{1} & G_{2} & {G_{3}\mspace{14mu} \ldots \mspace{14mu} G_{n}} \\B_{1} & B_{2} & {B_{3}\mspace{14mu} \ldots \mspace{14mu} B_{n}}\end{bmatrix}} \right){\quad{\begin{bmatrix}c_{1} \\c_{2} \\c_{3} \\\ldots \\\ldots \\c_{n}\end{bmatrix} = {\left\lbrack Y_{in} \right\rbrack - {{\begin{bmatrix}Y_{1} & Y_{2} & {Y_{3}\mspace{14mu} \ldots \mspace{14mu} Y_{n}} \\u_{1} & u_{2} & {u_{3}\mspace{14mu} \ldots \mspace{14mu} u_{n}} \\v_{1} & v_{2} & {v_{3}\mspace{14mu} \ldots \mspace{14mu} v_{n}}\end{bmatrix}\begin{bmatrix}c_{1} \\c_{2} \\c_{3} \\\ldots \\\ldots \\c_{n}\end{bmatrix}}.}}}}}}} & (5)\end{matrix}$

Therefore,

$\begin{matrix}{\left\lbrack Y_{d} \right\rbrack = {\left\lbrack Y_{in} \right\rbrack - {\left\lbrack {Y_{1}Y_{2}Y_{3}\mspace{14mu} \ldots \mspace{14mu} Y_{n}} \right\rbrack {\quad{\begin{bmatrix}c_{1} \\c_{2} \\c_{3} \\\ldots \\\ldots \\c_{n}\end{bmatrix}.}}}}} & (6)\end{matrix}$

Thus, equation (6) clearly shows that using YUV as the input to theencoder/decoder in accordance with the principles of the presentinvention as configured in this embodiment, is identical to performingRCT.

Also, in accordance with the principles of the present invention asconfigured in an embodiment, a new 4:4:4 profile is added to the H.264standard, referred to herein as “Advanced 4:4:4 Profile withprofile_idc=166”. This new profile_idc may be added in the sequenceparameter header, and may be used in the macroblock layer header, aswell as the residual data header.

To support using the luma algorithm to code all three color components,some changes may be made to the residual data syntax. In addition,changes may also be made to the semantics of some of the elements in themacroblock header, residue data header, and so forth. In general, theexisting syntax for luma in the H.264 specification will remainunchanged and be used to code one of the three components. The changesare backward compatible. The detailed syntax and semantics changes aredescribed herein below.

A description will now be given regarding simulation results performedin accordance with the principles of the present invention as configuredin various embodiments.

Turning to FIGS. 6A and 6B, plots of average PSNR verses bit rate forATV intra-only are indicated generally by the reference numerals 600 and650, respectively.

Turning to FIGS. 7A and 7B, plots of average PSNR verses bit rate for CTintra-only are indicated generally by the reference numerals 700 and750, respectively.

Turning to FIGS. 8A and 8B, plots of average PSNR verses bit rate for DTintra-only are indicated generally by the reference numerals 800 and850.

Turning to FIGS. 9A and 9B, plots of average PSNR verses bit rate forMIR_HD intra-only are indicated generally by the reference numerals 900and 950, respectively.

Turning to FIGS. 10A and 10B, plots of average PSNR verses bit rate forRT intra-only are indicated generally by the reference numerals 1000 and1050, respectively.

Turning to FIGS. 11A and 11B, plots of average PSNR verses bit rate forSTB_HD intra-only are indicated generally by the reference numerals 1100and 1150.

In particular, FIGS. 6A, 7A, 8A, 9A, 10, and 11A illustrate test resultsfor the proposed Advanced 4:4:4 profile (indicated and preceded by theterm “new”) versus approximation results corresponding thereto.Moreover, FIGS. 6B, 7B, 8B, 9B, 10B, and 11B illustrate test results forthe proposed Advanced 4:4:4 profile (indicated and preceded by the term“new”) versus JPEK2k.

In all of FIGS. 6A, 6B through 11A, 11B, the PSNR is indicated indecibels (dB) and the bit rate is indicated in bits per second (bps).ATV, CT, DT, MIR, RT, STB are the names of the test clips.

All JVT/FRExt test sequences described in JVT-J042, Film-Originated TestSequences, were used in the tests. They are all 4:4:4 10 bit filmmaterial and each clip has 58 frames.

The proposed advanced 4:4:4 profiles were implemented in the JVTReference software JM9.6. Both intra-only and IBBP coding structure wereused in the tests. The quantization parameter was set at 6, 12, 18, 24,30, and 42 for each of the R-D curves. The RD-optimized mode selectionwas used.

The proposed Advanced 4:4:4 Profile was also compared with the resultsthat were done by running the reference software with theYUVFormat=0(4:0:0) on every individual input component. Three separateindividual compressed bit counts were simply added together to get thetotal compressed bits for calculating the compressed bit rate.

Regarding JPEG2k, KaKadu V2.2.3 software was used in the tests. The testresults were generated by using 5 levels of wavelet decompression withthe 9/7-tap bi-orthogonal wavelet filter. There was only one tile perframe and the RD-Optimization for a given target rate was also used.

All of the PSNR measurements were done in the RGB domain. Average PSNR,defined as (PSNR(red)+PSNR(green)+PSNR(blue))/3, is used to compare theoverall compression quality. This is mainly because the JPEG2kcompressed data are computed using an unknown rate control algorithmprovided by the software. For some cases, the RGB PSNR values are quitefar apart from each other, especially when the JPEG2k color transformwas used.

The compression comparison was performed as follows:

-   -   New1: the proposed Advanced 4:4:4 Profile with a single        prediction mode.    -   New3: the proposed Advanced 4:4:4 Profile with three prediction        modes.    -   RCT-OFF: RGB input with RCT=off.    -   RCT-ON: RGB input with RCT=on.    -   YCOCG: RGB to YCOCG conversion was done outside the codec. Then        the converted YCOCG was used as the input to the JVT software.    -   R+G+B: Proposed method approximated by compressing the R, G, and        B signals separately.    -   Y+CO+CG: Proposed method approximated by compressing the        converted Y, CO, and CG signals separately.    -   J2k_RGB: The JPEG2k compression was done in the RGB domain. The        JPEG2k color transform was turned off.    -   J2k_YUV: The JPEG2k compression was done in the YUV domain. The        JPEG2k color transform was used.

According to the test results, an implementation in accordance with theprinciples of the present invention as configured in an embodiment, ingeneral, is very similar to JPEG2k in terms of overall compressionefficiency. In some cases, it is even slightly better.

Further, an implementation in accordance with the principles of thepresent invention as configured in an embodiment, provides significantlygreater performance (compression) than the current High 4:4:4 Profilefor quality above 40 dB (PSNR). Specifically, New1-YCOCG or New3-YCOCGis better than YCOCG and RCT-ON; New1-RGB or New3-RGB is better thanRCT-OFF. At a PSNR equal to and greater than 45 dB (PSNR), the averageimprovement in the average PSNR is more than 1.5 dB. In the lastexample, the improvement can be translated to more than 25% bit savingsat a PSNR equal to 45 dB.

According to the test results, it seems that color transforms will helpthe coding performance when the content is more color saturated, such asTP, RT. That is, if the color is neutral and less saturated, coding inthe RGB domain might be the right choice. The above observation isindependent from what color transform is used.

Comparing the results of New1-YCOCG or New3-YCOCG and JPEG-2k_YUV, ithas been observed that the performance of a specific color transform interms of improving coding efficiency is very content dependent. Nosingle color transform is always the best. Therefore, our data confirmedthat having a color transform, such as RCT, inside the encoding (ordecoding) loop might not be a good idea. Instead, performing the colortransform, if it is necessary, outside the encoder/decoder could makethe entire compression system provide a better and more robustperformance.

Comparing YCOCG with RCT-ON, the test results do not show any codingefficiency improvement from RCT. In addition, it should be noted thatrunning the reference software with the RCT turned on significantlyincreased the coding time. The running time was more than 2.5 timeslonger.

A description will now be given regarding syntax and semantics changesin accordance with the principles of the present invention as configuredin an embodiment.

Turning to FIG. 12, a table for H.264 sequence parameter syntax isindicated generally by the reference numeral 1200. Changes to the syntaxin accordance with the principles of the present invention as configuredin an embodiment, are indicated by italic text.

Turning to FIG. 13, a table for H.264 residual data syntax is indicatedgenerally by the reference numeral 1300. Additions/changes to the syntaxin accordance with the principles of the present invention as configuredin an embodiment, are indicated by italic text. In the table 1300, theluma section in the residual data header along with some necessary textmodifications are repeated twice to support the luma1 and luma2,respectively.

As noted above, the above described first combined embodiment wasevaluated and tested by implementing the present principles in the JVTreference software JM9.6. The test results marked with New1-RGB orNew1-YCOCG represent the first combined embodiment.

As noted above, in accordance with the principles of the presentinvention as configured in an embodiment, a set (or subset) of three (3)restricted spatial predictors is utilized for the component channels(e.g., RGB, YUV, YCrCb formats, and so forth) instead of a singlespatial prediction mode. Moreover, as noted above, this embodiment maybe combined with other embodiments described herein, such as, e.g., theuse of only the luma coding algorithm to code all three componentchannels of content and/or the use of color transformation as apre-processing step.

A description will now be given regarding the above described secondcombined embodiment involving the use of a set (or subset) of three (3)restricted spatial predictors for the color components, the use of onlythe luma coding algorithm to code all three color components, and theuse of color transformation as a pre-processing step (i.e., no RCTwithin the compression loop). Some variations of this embodiment willalso be described there with.

Turning to FIG. 14, an exemplary video encoding process with apre-encoding, color transform step are indicated generally by thereference numerals 1400 and 1401, respectively.

It is to be appreciated that the pre-encoding, color transform block1401 includes blocks 1406, 1408, and 1410. Moreover, it is to beappreciated that the pre-encoding, color transform block 1401 isoptional and, thus, may be omitted in some embodiments of the presentinvention.

The pre-encoding, color transform block 1401 includes a loop limit block1406 that begins a loop for each block in an image, and passes controlto a function block 1408. The function block 1408 performs colorpre-processing of the video signal data of the current image block, andpasses control to a loop limit block 1410. The loop limit block 1410ends the loop. Moreover, the loop limit block 1410 passes control to aloop limit block 1412, the latter being included in the video encodingprocess 1400.

The loop limit block 1412 begins a loop for each block in the image, andpasses control to a function block 1415. The function block 1415 forms amotion compensated or spatial prediction of the current image blockusing a common predictor for each color component of the current imageblock, and passes control to a function block 1420. The function block1420 subtracts the motion compensated or spatial prediction from thecurrent image block to form a prediction residual, and passes control toa function block 1430. The function block 1430 transforms and quantizesthe prediction residual, and passes control to a function block 1435.The function block 1435 inverse transforms and quantizes the predictionresidual to form a coded prediction residual, and passes control to afunction block 1445. The function block 1445 adds the coded residual tothe prediction to form a coded picture block, and passes control to anend loop block 1450. The end loop block 1450 ends the loop and passescontrol to an end block 1455.

Turning to FIG. 15, an exemplary video decoding process with apost-decoding, inverse color transform step are indicated generally bythe reference numerals 1500 and 1560, respectively.

It is to be appreciated that the post-decoding, inverse color transformblock 1560 includes blocks 1562, 1564, 1566, and 1568. Moreover, it isto be appreciated that the post-decoding, inverse color transform block1560 is optional and, thus, may be omitted in some embodiments of thepresent invention.

The decoding process 1500 includes a loop limit block 1510 that begins aloop for a current block in an image, and passes control to a functionblock 1515. The function block 1515 entropy decodes the coded residual,and passes control to a function block 1520. The function block 1520inverse transforms and quantizes the decoded residual to form a codedresidual, and passes control to a function block 1530. The functionblock 1530 adds the coded residual to the prediction formed from acommon predictor for each color component to form a coded picture block,and passes control to a loop limit block 1535. The loop limit block 1535ends the loop and passes control to an end block 1540.

In some embodiments, the loop limit block 1535 optionally passes controlto the post-decoding, inverse color transform block 1560, in particular,the loop limit block 1562 included in the post-decoding, inverse colortransform block 1560. The loop limit block 1562 begins a loop for eachblock in an image, and passes control to a function block 1564. Thefunction block 1564 performs an inverse color post-processing of thevideo signal data of the current image block, and passes control to aloop limit block 1566. The loop limit block 1566 ends the loop, andpasses control to an end block 1568.

As noted above, a new profile (profile_idc=166) for the Advanced 4:4:4Profile is disclosed. This new profile may also be used for the secondcombined embodiment, with corresponding semantic and syntax changes asdescribed herein below for the second combined embodiment. This newprofile_idc is added in the Sequence Parameter Set and will be mainlyused in the subsequent headers to indicate that the input format is4:4:4 and all three input channels are coded similarly as luma.

To minimize the necessary changes to the H.264 standard, no newmacroblock type is disclosed for the Advanced 4:4:4 Profile. Instead,all of the macroblock types along with the associated coding parameterslisted in Table 7-11, Table 7-13, and Table 7-14 of the H.264 standardare still valid. For the case of intra macroblocks, all three inputchannels, luma, Cr, and Cb, will be encoded based on the MbPartPredModedefined in Table 7-11 of the H.264 standard. For example, anIntra_(—)4×4 macroblock in the Advanced 4:4:4 Profile means every inputcomponent channel may be encoded by using all of the 9 possibleprediction modes given in Table 8-2 of the H.264 standard. Forreference, in the current High 4:4:4 Profile, two of the channels for anIntra_(—)4×4 macroblock will be treated as chroma and only one of the 4possible intra prediction mode in Table 8-5 of the H.264 standard willbe used. For the B and P macroblocks, the changes made for the Advanced4:4:4 Profile occur at the interpolation process for the calculation ofthe reference pixel value at the fractional pixel location. Here, theprocedure described in Section 8.4.2.2.1 of the H.264 standard, Lumasample interpolation process, will be applied for luma, Cr, and Cb.Again for reference, the current High 4:4:4 Profile uses Section8.4.2.2.2 of the H.264 standard, Chroma sample interpolation process,for two of the input channels.

In the case when the CABAC is chosen as the entropy coding mode, twoseparate sets of context models identical to those currently defined forluma will be created for Cr and Cb. They will also be updatedindependently during the course of encoding.

Finally, in the embodiment, since there is no RCT block in the codingloop, the ResidueColorTransformFlag is removed from the sequenceparameter set in the Advanced 4:4:4 Profile.

Up to this point, most syntax changes occur in the residue data as shownin FIG. 13, where the original syntax for luma are repeated twice tosupport Cr and Cb in the proposed Advanced 4:4:4 profiles.

Regarding the H.264 macroblock layer table (not shown), semantic changesto the corresponding syntax include the following.

coded_block_pattern (Add). When chroma_format_idc is equal to 3 andcoded_block_pattern is present, CodedBlockPatternChroma shall be set to0. In addition, CodedBlockPatternLuma specifies, for each of the twelve8×8 luma, Cb, and Cr blocks of the macroblock, one of the followingcases: (1) All transform coefficient levels of the twelve 4×4 lumablocks in the 8×8 luma, 8×8 Cb and 8×8 Cr blocks are equal to zero; (2)One or more transform coefficient levels of one or more of the 4×4 lumablocks in the 8×8 luma, 8×8 Cb, and 8×8 Cr blocks shall be non-zerovalued.

A description will now be given regarding spatial prediction modeselection for the intra blocks in accordance with the second combinedembodiment (or the sole embodiment relating to the use of the set (orsubset) of three restricted spatial predictors).

For each component to choose its best MbPartPredMode and the subsequentbest spatial prediction mode independently, as in the case whileencoding each input channel separately, some new intra block types maybe added to Table 7-11 of the H.264 standard. As a result, a largeamount of changes to the H.264 standard will be made. In an embodimentrelating to the second combined embodiment, the current mb_types remainunchanged and an alternative solution is provided. In the embodiment,the three input channels are restricted to be encoded with the sameMbPartPredMode or macroblock type. Then, a small amount of new elementsare added into the Macroblock Prediction Syntax to support threeseparate prediction modes. Therefore, each component can stilltheoretically choose its best spatial prediction mode independently inorder to minimize the prediction error for each component channel. Forexample, assuming an Intra_(—)4×4 macroblock is chosen as the mb_type,luma, Cr, or Cb could still find its own best spatial prediction mode inTable 8-2 in Section 8.3.1.1 of the H.264 standard such as, e.g.,Intra_(—)4×4_Vertical for luma, Intra_(—)4_(—)4_Horizontal for Cr, andIntra_(—)4×4_Diagonal_Down_Left for Cb.

Another approach, relating to the first combined embodiment describedabove, is to constrain all three input channels to share the sameprediction mode. This can be done by using the prediction informationthat is currently carried by the existing syntax elements, such asprev_intra4×4_pre_mode_flag, rem_intra4×4_pred_mode,pre_intra8×8_pred_mode_flag, and rem_intra8×8_pred_mode, in theMacroblock Prediction syntax. This option will result in less change tothe H.264 standard and some slight loss of the coding efficiency aswell.

Based on the test results, using three prediction modes could improvethe overall coding performance by about 0.2 dB over the first combinedembodiment.

Turning to FIG. 16, a table for H.264 macroblock prediction syntax isindicated generally by the reference numeral 1700. For reference, themodified Macroblock Prediction Syntax to support using the threeprediction modes is listed below, where:

prev_intra4×4_pred_mode_flag0 and rem_intra4×4_pred_mode0 are for luma;

prev_intra4×4_pred_mode_flag1 and rem_intra4×4_pred_mode1 are for Cr;

prev_intra4×4_pred_mode_flag2 and rem_intra4×4_pred_mode2 are for Cb;

A description will now be given regarding simulation results performedin accordance with the principles of the present invention as configuredin an embodiment, for the second combined embodiment.

All JVT/FRExt test sequences described in JVT-J042, Film-Originated TestSequence, JVT-J039 (Viper). They are all 4:4:4 10-bit materials and eachclip has 58 frames.

The proposed algorithm was implemented in the JVT Reference softwareJM9.6 and the modified software was used in the tests. Both Intra-onlyand IBRrBP were tested. Here, “Br” means the recorded B pictures. Theintra-only case was done for all of the sequences with the quantizationparameter equal to 6, 12, 18, 24, 30, 36 and 42. Due to the large amountof time involved in the simulation, the IBRrBP GOP structure was onlydone for the film clips with a quantization parameter equal to 12, 18,24, 30 and 36. According to the discussion in the 4:4:4 AHG, thefollowing key parameters were used in the tests:

-   -   SymbolMode=1    -   RDOptimization=1    -   ScalingMatrixPresentFlag=0    -   OffsetMatrixPresentFlag=1    -   QoffsetMatrixFile=“q_offset.cfg”    -   AdaptiveRounding=1    -   AdaptRndPeriod=1    -   AdaptRndChroma=1    -   AdaptRndWFactorX=8    -   SearchRange=64    -   UseFME=1

Regarding JPEG2k, KaKadu V2.2.3 software was used in the tests. The testresults were generated by using 5 levels of wavelet decompression withthe 9/7-tap bi-orthogonal wavelet filter. There was only one tile perframe and the RD-Optimization for a given target rate was also used.

The PSNR measurements were primarily calculated in the original colordomain of the source contents, which is RGB for the clips describedabove. Average PSNR, defined as (PSNR(red)+PSNR(green)+PSNR(blue))/3, isused to compare the overall compression quality.

The compression comparison was performed as follows:

New1: the proposed Advanced 4:4:4 Profile with a single prediction mode.

New3: the proposed Advanced 4:4:4 Profile with three prediction modes.

RCT-OFF: RGB input with RCT=off.

RCT-ON: RGB input with RCT=on.

YCOCG: RGB to YCOCG conversion was done outside the codec. Then theconverted YCOCG was used as the input to the JVT software.

R+G+B: Proposed method approximated by compressing the R, G, and Bsignals separately.

Y+CO+CG: Proposed method approximated by compressing the converted Y,CO, and CG signals separately.

JPEG2k_RGB: The JPEG2k compression was done in the RGB domain. TheJPEG2k color transform was turned off.

JPEG2k_YUV: The JPEG2k compression was done in the YUV domain. TheJPEG2k color transform was used.

For the Intra-Only case, the proposed Advanced 4:4:4 Profile inaccordance with the present principles is very similar to JPEK2k interms of overall compression efficiency. In some cases, it is evenslightly better.

The approach in accordance with the principles of the present invention,is clearly better than the current High 4:4:4 Profile. At a PSNR equalto and greater than 45 dB (PSNR), the average improvement in the averagePSNR is more than 1.5 dB. In some case, the improvement can betranslated to more than 25% bit savings at a PSNR equal to 45 dB.

Even with the same block type, using three prediction modes is slightlybetter than a single one. However, more syntax and semantic changes maybe utilized.

A description will now be given of some of the many attendantadvantages/features provided by the principles of embodiments of thepresent invention.

The test results demonstrate that the proposed Advanced 4:4:4 Profile,utilizing the improvements corresponding to the principles of thepresent invention, delivers improved performance when compared to thecurrent High 4:4:4 Profile. The performance gain is significant. Inaddition, moving the color transform outside the codec will make thearchitecture of the codec consistent among all of the color formats. Asa result, it will make the implementation easier and reduce the cost. Itwill also make the codec more robust in terms of selecting the optimumcolor transform for achieving better coding efficiency. Also, theproposed approach does not add any new coding tools and requires onlysome slight changes to the syntax and semantics.

Thus, in accordance with the principles of the present invention asconfigured in an embodiment, a method and apparatus are provided forvideo encoding and decoding. Modifications to the existing H.264standard are provided which improve performance beyond that currentlyachievable. Moreover, performance is improved even beyond JPEG-2000 forhigh quality applications. In accordance with the principles of thepresent invention as configured in an embodiment, significant 4:4:4coding performance improvements in the H.264 standard can be achieved byusing the luma coding algorithm to code all of the three colorcomponents of 4:4:4 content. That is, no new tools are necessary for theluma (or chroma, which is not used) compression algorithm. Instead, theexisting luma coding tools are utilized. Further, syntax and semanticchanges to the current 4:4:4 profile may be implemented in accordancewith the present principles to support the luma coding of all threecomponent channels. In tests conducted in accordance with an embodimentof the present invention, when the source content has lots of spatialtextures and edges, the spatial prediction tools used in luma clearlyexhibited their superior performance to those used in chroma. For someof the test sequences, when every color component was encoded as luma,more than a 30% bit reduction was observed at a compressed qualitygreater than or equal to 45 dB(Average PSNR).

It is to be appreciated that while the present invention has primarilybeen described herein with respect to video signal data sampled usingthe 4:4:4 format of the H.264 standard, the present invention may alsobe readily implemented with respect to video signal data sampled usingother formats (e.g., the 4:2:0 format and/or the 4:2:2 format) of theH.264 standard, as well as other video compression standards. Given theteachings of the present invention provided herein, these and othervariations of the present invention may also be readily implemented byone of ordinary skill in this and related arts, while maintaining thescope of the present invention.

These and other features and advantages of the present invention may bereadily ascertained by one of ordinary skill in the pertinent art basedon the teachings herein. It is to be understood that the teachings ofthe present invention may be implemented in various forms of hardware,software, firmware, special purpose processors, or combinations thereof.

Most preferably, the teachings of the present invention are implementedas a combination of hardware and software. Moreover, the software may beimplemented as an application program tangibly embodied on a programstorage unit. The application program may be uploaded to, and executedby, a machine comprising any suitable architecture. Preferably, themachine is implemented on a computer platform having hardware such asone or more central processing units (“CPU”), a random access memory(“RAM”), and input/output (“I/O”) interfaces. The computer platform mayalso include an operating system and microinstruction code. The variousprocesses and functions described herein may be either part of themicroinstruction code or part of the application program, or anycombination thereof, which may be executed by a CPU. In addition,various other peripheral units may be connected to the computer platformsuch as an additional data storage unit and a printing unit.

It is to be further understood that, because some of the constituentsystem components and methods depicted in the accompanying drawings arepreferably implemented in software, the actual connections between thesystem components or the process function blocks may differ dependingupon the manner in which the present invention is programmed. Given theteachings herein, one of ordinary skill in the pertinent art will beable to contemplate these and similar implementations or configurationsof the present invention.

Although the illustrative embodiments have been described herein withreference to the accompanying drawings, it is to be understood that thepresent invention is not limited to those precise embodiments, and thatvarious changes and modifications may be effected therein by one ofordinary skill in the pertinent art without departing from the scope orspirit of the present invention. All such changes and modifications areintended to be included within the scope of the present invention as setforth in the appended claims.

1. A video encoder for encoding video signal data for an image block,the video encoder comprising an encoder (100) for encoding all colorcomponents of the video signal data using a common predictor.
 2. Thevideo encoder of claim 1, wherein the common predictor is a lumapredictor used for both luma and chroma components of the video signaldata.
 3. The video encoder of claim 1, wherein said encoder (100) uses acommon spatial prediction mode for all of the color components of thevideo signal data.
 4. The video encoder of claim 3, wherein the commonspatial prediction mode is set by prev_intra8=8_pred_mode_flag,rem_intra8×8_pred_mode, prev_intra4×4_pred_mode_flag, andrem_intra4×4_pred_mode parameters of the International TelecommunicationUnion, Telecommunication Sector H.264 standard.
 5. The video encoder ofclaim 1, wherein said encoder (100) uses common interpolation filtersfor B and P frames for all of the color components of the video signaldata.
 6. The video encoder of claim 1, wherein said encoder (100)encodes all of the color components of the video signal data withoutapplying a residual color transform thereto.
 7. The video encoder ofclaim 1, wherein sampling of the video signal data corresponds to any ofthe 4:4:4, 4:2:2 and 4:2:0 formats of the InternationalTelecommunication Union, Telecommunication Sector H.264 standard.
 8. Amethod for encoding video signal data for an image block, the methodcomprising encoding (315) all color components of the video signal datausing a common predictor.
 9. The method of claim 8, wherein the commonpredictor is a luma predictor used for both luma and chroma componentsof the video signal data.
 10. The method of claim 8, wherein a commonspatial prediction mode is used for all of the color components of thevideo signal data.
 11. The method of claim 10, wherein the commonspatial prediction mode is set by prev_intra8×8_pred_mode_flag,rem_intra8×8_pred_mode, prev_intra4×4_pred_mode_flag, andrem_intra4×4_pred_mode parameters of the International TelecommunicationUnion, Telecommunication Sector H.264 standard.
 12. The method of claim8, wherein common interpolation filters are used for B and P frames forall of the color components of the video signal data.
 13. The method ofclaim 8, wherein said encoding step encodes all of the color componentsof the video signal data without applying a residual color transformthereto.
 14. The method of claim 8, further comprising performing (308)a color transform on the video signal data in a pre-processing stepprior to said encoding step.
 15. The method of claim 8, wherein samplingof the video signal data corresponds to any of the 4:4:4, 4:2:2 and4:2:0 formats of the International Telecommunication Union,Telecommunication Sector H.264 standard.